Barnabus "Barney" Stinson (born 1974-76) first met Ted Mosby in MacLaren's Pub in 2001, and since meeting him, he has been a big part of the gang and believes he's Ted's best friend. Before slowly wanting to settle down, he was a serial womanizer who could not stand the idea of commitment and would do extremely elaborate acts and lies purely to sleep with other women. His unique personality and elaborate techniques for seducing women are a constant source of humor (typically for Marshall), amazement (typically for Ted), and disgust (typically for Lily) to the rest of the group. Though he can be really mean to some of the women he has one night stands with, he has shown he can be very kind and loving to his friends as seen in Sandcastles in the Sand with Robin and in Sweet Taste of Liberty with Ted, and traveling to San Francisco to convince Lily to get back together with Marshall. He can also go very far to help a friend in trouble such as with Robin in The Possimpible. As of Last Forever - Part One, he is divorced to Robin.

Barney was born sometime between 1974 and 1976 and grew up in Staten Island.Barney was raised by his single mother, Loretta Stinson, with his older brother, James. James and Barney asked their mother why they had different skin colors, but she would either lie to them with impossible and illogical reasons or attempt to change the subject. Barney would also ask his mother who his father was. Eventually, she would tell Barney that Bob Barker was his father.

Before the start of the series and before he met the rest of the gang, Barney was somewhat of a hippie. He wanted to join the Peace Corps, was disgusted when men treated women like objects, and wished to wait to lose his virginity to his college girlfriend, Shannon, until after the two married. His personality radically changed when he caught Shannon cheating on him with a man named Greg. His current mannerisms and dress sense are based on the man who took Shannon away from him. Barney is now an extreme womanizer, not content unless he is pursuing his latest conquest. He has no problem lying or using extremely ridiculous methods to charm women. Along with being proud and very open about his collection of pornography, he doesn't see anything wrong about secretly video taping and taking pictures of the women he sleeps with. He did mention to Robin that he watches the videos to study himself more, like how athletes study game tapes. He also seems to dislike the idea of owning a "little, black book" and instead has a scrapbook filled with the pictures of women he has slept with. Barney does not care at all what happens to his one-night stands as long as he doesn't have to see or talk to them again.